An antenna apparatus is provided in various kinds of communication devices, and transmits and receives radio waves of a predetermined frequency band. The growing popularity and application range of portable radio devices typified by mobile phones has led to a great increase in demand for wideband capability of portable radio device antennas, and a trend associated with the rapidly expanding use of portable radio devices is for the number of channels in one wireless communication system to be insufficient. Consequently, consideration has been given to the combined use of mutually different wireless communication systems using mutually different frequency bands to secure a necessary number of channels, and major advances in techniques for reducing size and weight have led to the development of terminals enabling two different kinds of wireless communication systems to be used by a single portable radio device. Moreover, consideration has been given to the need for a bandwidth of several hundred MHz in the UHF band for reception of terrestrial digital broadcasts, for example. Furthermore, reducing the size of a radio apparatus by supporting a plurality of WLAN (Wireless Local Area Network) standards using different frequency bands by means of a single antenna requires, for example, an antenna covering the 2.4 GHz and 5.2 GHz bands.
In communications between a mobile station and base station in a mobile communication system, fading often occurs in which the received signal level fluctuates according to various radio wave propagation environments. Effective measures against fading include antenna selective diversity and combined diversity. With antenna selective diversity, a plurality of normal antennas are installed, and communication is performed by switching to an antenna with good conditions when reception degrades due to fading. For example, there are antenna selective diversity apparatuses in a TDMA (Time Division Multiple Access) communication system in which the same frequency is shared by a plurality of users by means of time division.
Patent Document 1 discloses a mobile wireless telephone that performs diversity operation only when using an external antenna in order to reduce the size and standby current of a diversity mobile wireless telephone.
Patent Document 2 discloses an antenna switching circuit and communication device that provide an antenna switching circuit with little signal loss capable of performing antenna diversity independently for each of a plurality of communication systems by using a duplexer.
FIG. 1 is a drawing showing a configuration of a conventional portable radio device having a plurality of radio sections capable of diversity operation.
In FIG. 1, portable radio device 1 having a plurality of radio sections capable of diversity operation is equipped with first through third main antenna apparatuses 11 through 13, first through third radio sections 21 through 23 connected to first through third main antenna apparatuses 11 through 13 respectively, and first through third sub-antenna apparatuses 31 through 33 for diversity operation of first through third radio sections 21 through 23.
First through third radio sections 21 through 23 are radio sections capable of diversity operation that perform diversity operation by performing antenna switching between first main antenna apparatus 11 and first sub-antenna apparatus 31, second main antenna apparatus 12 and second sub-antenna apparatus 32, and third main antenna apparatus 13 and third sub-antenna apparatus 33, connected to the respective radio sections.
First radio section 21 is an HSDPA (High Speed Downlink Packet Access) mobile phone radio section that transmits and receives usable frequency f1 radio waves. An HSDPA diversity receiving apparatus in a W-CDMA system performs diversity reception, creates a delay profile on a branch-by-branch basis, and assigns fingers to received signals based on that delay profile.
Second radio section 22 is, for example, a digital TV tuner for one-segment broadcasting reception that receives a usable frequency f2 radio wave.
Third radio section 23 is a WLAN radio section that transmits and receives usable frequency f3 radio waves. The above combination of radio sections 21 through 23 is just one example, and another example of above radio sections 21 through 23 is a UWB (Ultra Wideband) radio section capable of diversity operation.    Patent Document 1: Japanese Patent Application Laid-Open No. HEI 5-316010    Patent Document 2: Japanese Patent Application Laid-Open No. 2004-7162